[Bug c++/109529] New: the r-value volatile object is not accepted by the l-value volatile constant argument.

[Bug c++/109529] New: the r-value volatile object is not accepted by the l-value volatile constant argument.

[lisp2d at rambler dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109529

            Bug ID: 109529
           Summary: the r-value volatile object is not accepted by the
                    l-value volatile constant argument.
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lisp2d at rambler dot ru
  Target Milestone: ---

void funy(int const &){}
void fun(int volatile const &){}
int main(){
  int y ;
  funy(y); // good
  funy(static_cast<int && >(y)); // good
  funy(static_cast<int const && >(y)); // good
  int volatile x ;
  fun(x); // good
  fun(static_cast<int volatile && >(x)); // error
  fun(static_cast<int volatile const && >(x)); // error
}

[Bug c++/109529] the r-value volatile object is not accepted by the l-value volatile constant argument.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109529

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
only const references can be bound to temporaries. const volatile references
cannot be bound to a temporary.

That is even this is invalid code:
```
int main(){
  const volatile int & a = 1;
}
```

[Bug c++/109529] the r-value volatile object is not accepted by the l-value volatile constant argument.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109529

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Since `static_cast<int volatile && >(x)` is considered rvalue and `int volatile
const &` needs to be bound, it will not be bound to a temporary (rvalue) which
is produced by the rvalue reference.

In the non-volatile case, well it is a const reference which can be bound to a
temporary value (rvalue) and that temp in this case will end its lifetime after
the end of the statement (after the ;).

[Bug c++/109529] the r-value volatile object is not accepted by the l-value volatile constant argument.

[lisp2d at rambler dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109529

--- Comment #3 from Lisp2D <lisp2d at rambler dot ru> ---
(In reply to Andrew Pinski from comment #2)
> Since `static_cast<int volatile && >(x)` is considered rvalue and `int
I can't find a reason anywhere in the standard why the volatile property
prevents conversion from `&&` to `const &`.

[Bug c++/109529] the r-value volatile object is not accepted by the l-value volatile constant argument.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109529

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
https://stackoverflow.com/questions/40193008/why-a-const-volatile-reference-cannot-be-bound-to-an-rvalue-reference

[Bug c++/109529] the r-value volatile object is not accepted by the l-value volatile constant argument.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109529

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Basically  [dcl.init.ref]/5 .

[Bug c++/109529] the r-value volatile object is not accepted by the l-value volatile constant argument.

[lisp2d at rambler dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109529

--- Comment #6 from Lisp2D <lisp2d at rambler dot ru> ---
(In reply to Andrew Pinski from comment #4)
> https://stackoverflow.com/questions/40193008/why-a-const-volatile-reference-

stackoverflow offers to link an rvalue reference to a variable for this. But I
think this is historical stupidity.

  int volatile && rx =
    static_cast < int volatile && > ( x ) ;
  int volatile const & lx = rx ;  
  fun(lx);

[Bug c++/109529] the r-value volatile object is not accepted by the l-value volatile constant argument.

[lisp2d at rambler dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109529

--- Comment #7 from Lisp2D <lisp2d at rambler dot ru> ---
.. or

  int volatile && rx = static_cast < int volatile && > ( x ) ;
  fun(rx);